Because it suggests that if you’re popping over to England you might want to stock up on Viagra (“you can skip the oysters (and other aphrodisiac foods) at the grocery store — and head straight to the medicine aisle”), which according to a story that Tres also linked, is an idea that carries health risks.

From Tres Sugar 1:45 pm Grab Bag link:
"...the recreational use of Viagra by young men without erectile dysfunction is rising. In fact, its use by men aged 18-45 has increased three-fold since its release in 1998. Many of these men have no physiologic problems, and are using the drug for presumed sexual performance enhancement.
So, are these men enhanced? Are they Superstars of Virility? Not really. First, let’s look at what you can expect. Viagra will not enlarge your penis. It won’t improve your stamina. And it won’t decrease premature ejaculation. It will, however, decrease your refractory time, the time required to achieve a subsequent erection after ejaculation. And it will allow a firmer erection with less stimulation. So, you might be able to have sex more times in the same night, and with a partner to whom you are less attracted. Sound good?
Before you start popping the blue diamonds, understand that this male superpower comes at a cost as well, and I am not just referring to the stiff price of the pill itself. Common side effects include headache, increased heart rate, stuffy nose, facial flushing, blurred vision, and heartburn. Most men will experience one or more of these symptoms. There’s also a very low risk for priapism, an abnormal erection that won’t go down. It may be rare, but treatment for this complication begins with a large needle in the side of the penis, and can end in permanent impotence. And if you’ve watched TV in the last ten years, you may already be familiar with the interaction between Viagra and nitrate medications. It’s fairly unlikely that a young male would be taking a nitrate medication (usually used for cardiac-related chest pain), but the combination can cause a fatal drop in blood pressure.
Still willing to take the plunge, Casanova? As a doctor, I would advise against it. But since I know the number of people who actually follow their doctor’s recommendations, I would be remiss if I didn’t give you some advice. First off, please see a doctor before trying any medication. This is especially true if you have a history of cardiovascular problems or strokes.
Second, don’t combine the medication with alcohol or street drugs. Although there are not any well-documented interactions between Viagra and alcohol or illicit narcotics, combining multiple drugs is rarely a good idea. And there are case reports of cocaine and ecstasy causing priapism — why compound that risk?
Moreover, while under the influence of mind altering substances, “limp dick” often prevented a man from undertaking some poorly-conceived (and often risky) behavior. Viagra just might enable you to make some mistakes you’ll later regret. Thirdly, while its use is generally safe for the young male, repeated use can potentially lead to psychological addiction. Just like any performance-enhancing drug or routine, the user can come to mentally depend upon it, even if it is not physically needed. In my mind, this is the single greatest risk of recreational Viagra use.
Finally, really try to understand that Viagra most certainly won’t make you a better lover. Any man worth his salt, and all women, knows that the height of sexual ecstasy is not some dude endlessly pounding away, despite what those male porn stars would have you believe."
http://www.emandlo.com/2010/09/dear-dr-joe-is-it-save-to-take-viagra-just-for-fun/